Optically switchable windows exhibit a controllable and reversible change in an optical property when placed in a different state, which may be driven by a controllable stimulus such as a voltage change. The optical property is typically one or more of color, transmittance, absorbance, and reflectance. Electrochromic devices are sometimes used in optically switchable windows. One well-known electrochromic material, for example, is tungsten oxide (WO3). Tungsten oxide is a cathodic electrochromic material in which a coloration transition, transparent to blue, occurs by electrochemical reduction.
Electrically switchable windows, whether electrochromic or otherwise, may be used in buildings to control transmission of solar energy. Switchable windows may be manually or automatically tinted and cleared to reduce energy consumption, by heating, air conditioning and/or lighting systems, while maintaining occupant comfort.
Only recently have designers begun developing control and power systems for buildings having many electrically tintable windows. As a consequence, many developments are required before such systems can operate reliably and approach their potential.